can a flashlight move in space when we turn?

Answer 1

Yes, the flashlight would feel a net force acting in the opposite direction as the light is shining.

Each photon emitted from the flash light carries with it a certain (albeit small) amount of momentum. Due to the law of conservation of momentum...the momentum of the photons in one direction would need to be canceled out by a change in momentum in the other direction. The flash light would feel a force (causing a change in momentum) to push it the opposite direction the light is traveling. This net force would cause the flash light to accelerate in the direction of the force and thus experience a change in velocity.
It would be like a rocket engine in a way...the rocket pushes out propellant in one direction and accelerate in the other, but in the flashlight case, the flight light would push light out and not a rocket fuel.

The energy (E) contained within a photon of a particular frequency (v) is given as,
E = hv
Where g is Planck's constant.
The momentum (p) of a photon with a given energy (E) is given as,
p = E/c
Where c is the speed of light in a vacuum.

h = 6.626068 × 10^-34 m^2 * kg / s
c = 299,792,458 m/s

Answer 2

While mrjeffy32 has a nice theoretical answer, the question is still yes, it will. Until absorbed by matter in the void we call space, the light energy produced by the heated filament in the flashlight will travel in a straight line, at roughly the speed of light, or 186,000 miles per second. Held stationary by the person holding it, and left on for any period of time, the light beam would make an arc in the sky as the earth turns in it's rotation.

Answer 3

A flashlight will move whichever way you turn it whether on earth or in space.

Or is this another poorly written question that missed out the last word "on"?

The answer is yes it will move. The light imparts a tiny momentum, however it is so small that you probably won't be able to measure it.

Answer 4

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